Magnetic switch for traffic detectors



1942- s. EJSTRI CKLAND MAGNETIC SWITCH FOR TRAFFIC DETECTORS Filed June'7, 1941 IIIIIIIIIIIIIIIII IIIIIIIIIII II I IN V EN TOR. Genoa/v E.Ste/cm ND nil;

A TTOENEYS.

Patented Nov. 24, 1942 UNITED STATES PATENT OFFICE MAGNETIC SWITCH FORTRAFFIC DETECTORS 9 Claims.

The present invention relates to a magnetic switch for trailicdetectors, or more specifically for devices used in detecting theapproach or passing of motor vehicles, and is designed particularly foruse in service stations or the like to apprise an attendant of thepresence of a patron desiring service.

Many different types of devices have been used for producing an audibleor Visible signal upon the approach of an automobile to a servicestation, and the most commonly used types comprise fluid filled hoses orother mechanical means over which the automobile passes to create thedesired signal. These types are undesirable in that they are exposed andusually produce a hazard to pedestrians, who may stumble over them, andthey are subject to mechanical wear, and interfere with proper cleaningof the pavement or driveways in which they are situated. Variouselectrical signaling devices have also been proposed employing theprinciples of induction and magnetism, but are impractical because theyare It is the object of the present invention to provide a magneticswitch for a traflic detector which overcomes all of the disadvantagesset forth above, and which is relatively simple in construction. andinexpensive to manufacture, install and maintain. It is a further objectof the invention to provide a device of this character, in which thefriction of all moving parts is reduced to an absolute minimum, andwhich will be sensitive to the movement of a motor vehicle within areasonable distance of the point where it is installed, and regardlessof fixed magnetic bodies in its vicinity, or even of motor vehicleswhich have been brought to a stop in its immediate vicinity. A stillfurther object is the provision in a sensitive device of this kind ofmeans to prevent its operation by the movement in its vicinity of smallmagnetic bodies, or movement at a great distance from it of largemagnetic bodies, and to provide a device which will effect positiveclosing of a circuit upon passing of a motor vehicle without oscillatingin a manner to make and break the circuit repeatedly.

The manner in which these objects are at-- tained, as well as furtherobjects and advantages of the invention, are made apparent in the fol-Fig. 1 is a vertical transverse sectional View of a magnetic switchembodying the present invention;

Fig. 2 is an enlarged view in perspective portion of the mechanismillustrated in Fig. 1;

Fig. 3 is a perspective View of a modified form of the contact mechanismillustrated in Figs. 1 and 2; and

Fig. 4 is a sectional view illustrating the manner of use of the contactmembers shown in Fig. 3.

The magnetic switch of the present invention is shown as contained in ahousing l0, preferably cylindrical in shape, and closed by a covermember H, which may be sealed in place by any suitable means and which,if desired, may be constructed to admit to the interior of the housingan inert gas for example nitrogen under pressure to decrease arcingbetween electric contacts carried within the housing. A bar magnet I2 isdisposed within the housing and supported for oscillatory movement abouta central vertical axis therein. In order to maintain the axis of themagnet l2 vertical, regardless of any slight irregularity in theposition of the housing l0, and also to reduce to a minimum anyfrictional resistance to the turning of the magnet, it is supportedwithin a rectangular frame 13, which is suspended from the center of thecover H by a universal connection 54, as shown. The rectangular frame l3may, to facilitate perfect balance, be formed of two members similar tothat shown, disposed at right angles to each other and crossing at theircenters at the point of intersection of the axis about which the magnetoscillates. The magnet is secured, as by a screw I5, to the upper end ofan elongated cylindrical vertically disposed fioat It, made preferablyof very light non-magnetic material, and the magnet and float aresuspended for oscillation within the frame I3 between pivot bearings,one of which is shown at I! at the lower end of the float, and the otherof which is shown at IS. The upper bearing 18 which receives the pivotpin I9 is in the form of a metal block threaded into a di-electric block28, wh ch is retained centrally of the magnet by the same screw l5,which screws the magnet to the float It. The pin [9 is insulated fromthe frame l3 by a di-electric bushing 2!. The housing it] contains aliquid, as shown, which is preferably carbon tetra-chloride or otherliquid having a relatively high boiling point for liquids of thisgeneral character to prevent condensation, of high specific gravity, anda good di-electric in case it wets the contact points within'thehousing,

due to condensation or other causes. The housing is filled with thisliquid to a level at which its buoyant effect on the float IS, themagnet I2, and other parts carried thereby is sufficient to reduce to aminimum any pressure on the pivot bearings, about which the magnetoscillates. The elongated cylindrical float I 5, in this construction,presents the advantages that a great portion of its area may be immersedin the liquid without bringing the magnet or other parts too close tothe liquid, and also its outer cylindrical wall is, due to its shape, soclose to its axis of rotation that very little resistance is set up byfriction of liquid on its outer surface to oppose its turning movement.A vane 22, formed of light non-magnetic material, is immersed in theliquid and supported by an arm in the form of a light wire 23, which isformed at an angle, so that one end of it overlies the top of the magnetwhere it is supported by an eye 24, in a balanced position, while itsfree end extends into a small recess 25 in one side of the di-electricblock 20. An offset 26 is formed in the arm 23 to prevent its endwisemovement through the eye 24, and the eye is set in a di-electric block,shown in dotted lines at 21, so as to insulate it from the magnet.Adjacent its upper end the arm 23 carries a small metal plate 28,normally disposed in a vertical plane, and spaced between parallel metalplates 29, which project outwardly from the side of the di-electricblock 20, as best illustrated in Fig. 2. The guide wire 30 is supportedby the float l6 and looped at its end, as shown at Si in Fig. 2, withinthe downwardly extending portion of arm 23 to limit the magnitude of itsoscillatory movement. One of the plates 29 is connected by a wire, orother conductor 32, with the pivot bearing it, which preferably containssufiicient mercury to complete a circuit to the pivot pin 19, and thencethrough a wire 34 to a binding post 35, which extends through and isinsulated from the cover member H. The other of the plates 29 isconnected as by a wire 36 (see Figs. 1 and 2) with the float [6, whichthrough its lower pivot bearing, the frame I3, and universal connectioni4, completes a circuit to a binding post 3'1, which is not insulatedfrom the cover I I.

In practice the device described above is buried just below the surfaceof the pavement in a service station at whatever point in the drivewaythat it is desired to have the passing of an outomobile actuate asignal. As the effective range of the device is limited, it may benecessary in wide driveways to employ more than one device, and wherethere is more than one driveway the device may be employed in whatevernumber is necessary and desirable. The binding posts 35 and 3'1 areconnected as by conductors 49 and 4! in the switch circuit of a relaywhich controls an electric signal, such for example, as a bell orelectrically actuated gong (not shown) As these conductors 4E] and Mform the only connection with the signal, and as the electric currentnecessarily carried by them is small, they may be inexpensivelyconcealed by being embedded a slight distance in the pavement where itis necessary that they cross any part of the drive.

An automobile is, of course, a magnetic body, and possesses magneticpolarity. Hence when it passes the switch of the present inventionembedded slightly below the surface of the driveway, it oscillates thebar magnet 12, it being understood that this magnet normally assumesalignment with the terrestrial magnetic flux subnormal to again breakthe switch circuit.

ject to what deviation may be caused by proximate magnetic bodies. Theefiect on the magnetic bar l2 by a passing automobile is to cause it tooscillate about the vertical axis upon which it is suspended, and duringthis oscillation the vane 22 is carried with the bar, but its movementis resisted by the fluid in which it is immersed, with the consequencethat it effects swinging of its support 23 with a resultant turning ofthe small plate 28 about a longitudinal axis causing this plate toengage and close a circuit between the two contact plates 29. Thiseffects closing of the switch circuit, which includes the binding posts35 and 31 in the manner set forth above, and therefore actuates theelectric signal, which apprises the attendant of the service station ofthe presence of the automobile.

The present invention overcomes the undesirable repetition of switchclosing, which ordinarily results from oscillation of the magnet in adevice of this kind, because of the fact that the oscillations whichprecede return of the magnet to its normal position after passing of theautomobile are less forceful, and therefore permit the vane 22, whichalso acts as a damper to these movements, to remain substantially in itsvertical position, so that the plate 28 is not turned to a contactmaking position. Another advantage of o the structure shown herein isthat an automobile brought to a stop in the immediate vicinity of theswitch does not cause continued closing of the switch circuit eventhough it may hold the magnet bar 12 away from its normal position. Thisresults from the fact that after initial closing of the switch byswinging movement of the magnet bar, and retarded movement of the vane22, the vane which has been swung slightly away from its normal verticalposition gravitates to If a car remains parked adjacent the switch itacts as any other fixed magnetic body, and the position to which itdeflects the magnet part l2 then becomes normal, and any otherautomobile passing the switch will deflect the magnet bar from its new,or temporarily normal position, suillciently to actuate the switchthrough the medium of the vane 22 in the same manner as described above.

In Figs. 3 and 4 a modified form of the invention is illustrated,showing a structure in which the contact points of the switch areselfcleaning. In these figures the upper end of the member 23, whichsupports the vane 22 is guided in a pivot bar 45, which is formedDivotally with the head of a screw 46, and in this case serves to securethe magnet bar l2 to the float IS. The upper pivot pin 41, which isreceived by this bar, is embraced by a metallic sleeve 48, which isspaced from the pivot pin by a dielectric bushing 49. An arm 50, carriedby the upper horizontal portion of the member 23, which carries the vane22, supports a U-shaped contact member 5| in a position spaced slightlyfrom the sleeve 48. The sleeve 48 is connected by a wire 52 with onebinding post, which is included in the switch circuit (one binding post,not shown, which is included in the switch circuit) and a wire 53connects the pivot pin 41 with the other binding post, consequently,when the vane switches from its normal vertical position the U-shapedmember contacts the sleeve 48, and closes the switch circuit through themedium of the arm 50, the upper portion of the member 23, and the pivotpin 41. A positive electric connection between the pivot pin 41 and thearm 23 is preferably insured by a drop of mercury in the pivot bar 4-5.In this modified switch structure the contact is made by the contactmembers 48 and 5! during oscillatory movement of the magnet bar 12, withthe result that the consequent wiping action between contact pointsautomatically keeps them clean and bright.

In the normal operation of either of the two modifications disclosedherein the passage of an automobile will effect suiiiciently forcefuloscillation' of the magnet to close the switch twice; once on themovement of the magnet away from the normal and once again on its returnmovement. The oscillation will seldom, if ever, be sufficient to efiectthree or more closings of the switch.

Another advantage of the structures disclosed is that no foreignmagnetic body, such as an automobile jack or other garagemans tool leftin a position adjacent the switch will effect its operation because ofthe fact that the magnet will orient itself to the influence of theforeign body, and the vane will, under the force of gravity, assume itsnormal vertical position with the switch open, and a passing automobilewill produce the desired result upon the magnet in any position which itmay have been caused to assume.

The arm 23, which supports the vane while shown as supported pivotallyfrom above the magnet part 12, may as well be suspended from beneath thebar by changing the relative positions of the bar it, and thedi-electric block 20, as shown in Fig. 1, and various othermodifications in the construction and the arrangement of the severalparts herein shown and described may be made within the scope of theappended claims.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. A magnetic switch closing device comprising, a magnet adapted to beoscillated by a magnetic force in its vicinity, a vane carried by themagnet and supported for pivotal movement relative thereto and immersedin a liquid, and a switch actuated by pivotal movement of the vanerelative to the magnet, whereby resistance of the liquid to movement ofthe vane will actuate the switch upon movement of the magnet.

2. A magnetic switch closing device comprising, a magnet pivoted forswinging movement in a horizontal plane, and adapted to be oscillated bya magnetic force in its vicinity, a body of liquid underlying themagnet, 21. vane supported by the magnet for swinging movement anddepending into the liquid whereby pivotal movement of the magnet willcause swinging of the vane, and a switch closed by swinging of the vanerelative to the magnet.

3. In a magnetic switch closing device, a housing adapted to containliquid, a magnet disposed above the liquid level in the housing andadapted to be oscillated by the magnetic force in its vicinity, anelongated cylindrical vertically disposed float partially immersed inthe liquid and supporting the magnet at its upper end, and pivotbearings mounting the magnet and float and aligned with the verticalaxis of the float.

4. In a magnetic switch closing device, a housing adapted to containliquid, a magnet disposed above the liquid level in the housing andadapted to be oscillated by the magnetic force in its vicinity, anelongated cylindrical vertically disposed float partiall immersed in theliquid, and supporting the magnet at its upper end, and pivot bearingsmounting the magnet and float and aligned with the vertical axis of thefloat, and a support for said pivot bearings depending for free swingingmovement from the top of the housing.

5. In a magnetic switch closing device, a housing adapted to containliquid, a magnet disposed above the liquid level in the housing andadapted to be oscillated by the magnetic force in its vicinity, anelongated cylindrical vertically disposed float partially immersed inthe liquid and supporting the magnet at its upper end, and pivotbearings mounting the magnet and float and aligned with the verticalaxis of the float, a vane disposed in the liquid and pivotally supported relative to the magnet whereby it will swing upon oscillation ofthe magnet, and a switch adapted to be closed by swinging movement ofthe vane.

6. In a magnetic switch closing device, a magnet mounted for oscillationin a horizontal plane over a body of liquid and adapted to be oscillatedby a magnetic force in its vicinity, a vane depending from said magnetnormally vertically into said liquid and mounted for limited swingingmovement, and a switch adapted to be closed upon swinging of the vaneaway from vertical and opened upon return of the vane to its verticalposition.

'7. In a magnetic switch closing device, a bar magnet mounted foroscillation in a horizontal plane over a body of liquid and adapted tobe oscillated by a magnetic force in its vicinity, an arm pivotallymounted over and substantially parallel to the bar and having an enddepending into the liquid, a vane carried by said end wherebyoscillation of the magnet will swing the arm in its pivotal support, anda switch closed by such swinging of the arm.

8. In a magnetic switch closing device, a pivoted magnet adapted to beoscillated by a magnetic force in its vicinity, a pair of spaced contactplates fixed relative to the magnet, a pivoted plate disposed betweensaid spaced plates, a vane carried by the magnet and depending into aliquid whereby pivotal movement of the magnet will effect swinging ofthe vane, and means whereby such swinging of the vane will swing saidpivoted plate into bridging contact with said spaced contact plate.

9. A magnetic switch closing device comprising a pivoted magnet adaptedto be oscillated by a magnetic force in its vicinity, a vane supportedfor pivotal movement relative to the magnet, a switch, means wherebysaid relative movement of the vane and magnet will effect closing of theswitch, said vane being immersed in a body of liquid to damp itsmovement whereby upon movement of the magnet the vane will be retardedto produce the said relative movement of the vane and magnet and effectclosing of the switch.

GORDON E. STRICKLAND.

